Except most people with mental disorders don't want to kill anyone or at least they don't kill anyone. I know from personal experience because my ex-wife had bipolar disorder. Even though she was usually as sweet as she could be and most people who knew her loved her, just about anything could set her off in a rampage at just any moment. But, amazingly, in her 40 years, she has never gotten into a fight. Even though she had threatened people when she go into those fits of rage, as far as I know she has never physically seriously hurt anyone but herself. She attended a mental facility regularly and I got to know some of her fellow clients. This is how I know most of them would not kill anyone. Most of them were sweet people most of the time.

I understand what you're saying and something definitely goes wrong in a mind when someone wants to kill but it's like placing a poisonous snake and a common house cat in the same class. It seems like people are trying to justify killing to get a lighter sentence. "Ahhh, poor Johnny couldn't help it, he was abused as a child." My sister was abused as a child by my mother but she grew up to be a social worker with degrees in Psychology, Social Work and something else that I can't remember. She's never forgiven her mother who has apologized a number of times and is obviously sincerely as sorry as she can be and she had a rough childhood too and that's not to excuse how she abused my sister but murder is on a much deeper level of evil!